Modulated-wave transmission



R. A. HEISING MODULATED WAVE TRANSMISSION Original Filed Sept. 21. 1915 Z W f w v EA NI HIEEHIHG,

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. rgonlrzxiion filcrl September 231, 1915, Serial 1%. 513M. Pate EIi'o. 1,23 2%,562, Claim China 15,

may more?" 4 on tho. i, im'iilsronn A Hinsmo inc United Emtss, iding at in tin: couni'y of risscx, Stoke n, bass invented ccriaci'ai now rorcn'icnrs in biotin, orb ions? "iissions, oi which the foiiowing 4 VS .i i" a foil, cion, ccncisc, and exact descr ption. This .iiiVPl'ibiOli relates to sysiei'ns IO? tho proinctii'an and transom anon of nioduiwwi oscillations. ivioduiarcd osciiistions in. n *"c s 'c scnso are oscillations of given char J, one or more Whose cimroctcc :i in occordsncc with ins'bzn of a modulating (i'evicc )ecificriiiy, nodriiuxtion. ,n. in amplitudc or intonv high ircqucncy electrics Wave whom the mission occurs in cccoriiionce with sou d or eiocaricai waves of a relativsiy ion; cone-y,

l rior to this inveriion it, has i that if on oicctricsi or tbnion (ic'vicc oi the by H aving :in anodcq mic and an impciizrnco varying c 1S zassocisiicfi with su'i "bio gefcrobiy hiding a, tnnco iiroqocn 1m nn cnit 21in sourcc oi? on "1 qnomy osci .ntions will. be con+ l y srzitcci. iii;-

LiE-JO been known that o nfcrobonc o, "ruifasient ricvi is associctci """Lr suit in o, si )in, maninipeczincc tbs anode, or both 1 to the ca'tiiodc uc- A or onoiibio iroacncy Waves action upon the microphone or other oi rent shirt tbs amplitude or in.- tensity of the gcneratcd oscillations can bc made to vary to some extent in accordance with speech waves, so that time cnvcio'pc oi the higi' oqucnc); osciiiations will be a mom or ics: noricm'; i'c prescniuwm oi'i-tiic n'ioduizit'. *n

This inrcmi izn i an. object to pro i'ic io means whereby an improvcmcnt in tho quaiity the moduini'crl warns produced by such an orrimgcmcnt may T1 acted, Sailorsby casing me viii-int? tho high "fro oucncy no cs to be so gisrfc: a; inciion form can i.

ch moi-o wow-3 Kori: or

n lfiiviiieai and this connection filed 4%, Serial No 3%,4351.

moons "for this purpose is an energy dissipating; or resistance element of suitable voiuc scriaily included in too tuned circuit of the ii'icrmionic device. Similar results, bowl-var, can, be obtained by any equivalent moms which 'Wiii cause the envciope of the high frequency osciiiationsto pcriectly rcnodnco tho wove form oi the modulating waves.

The reason for the improved results obtained by the ab-ovcdescribed means is understood to be as follows when a thermionic oscillation generator or she ordinary typo is set in operation, tho intensity of the produced osciiiations buiifls up rapidly until tho high frequency cncrgy dissipated in the :ozn is equal to that produced from the (2% current source of energy provided. This condition is reached only when the os- Ciiiflil01;V CUII'BHiZ generated contains harnom'o frequencies in large proportions as compared with the fundamental or base frequency. The presence of these harmonics rcsuirs in iiighiy complicated rather than simple harmonic Wars form. When a inoduiairing device acts upon a tube so oscil- 21 snmii change in amplitude of the pirocincoci oscillations results also in a relax their large change in the proportion and numbcr of tho harmonics present and thus prodrwcs considerable changes in the high ancy wovc form. Such a process is orcnot one of changing a single high 'cqucncy Wave in accordance with a moduiaiing wzwc, but is ono of changing in a different degree each of a number of Waves of harmonic frequencies. Instead, therefore, of proibicing a. Wave form which accurately rcprotsnts tbo specch to be transmitted & g'cafly distorted Wave form rcsuliis which is very incificioni; for the transmission of speech.

By inciuding; a resistance of a proper Yaluc iii the osciiiaiion circuit the intensity of time nos'nmiiy produced oscillations is not ouiy L-;k1li(3(i but tho harmonics .arc'eliiniimtcd and, tho quality oi; speech transmitted c improvod. The envelope of the l ioncy waves is made to closely fol? ion: ihc wzwc form of the low frequency osciiiotions and H quality of modulation V/biio ixho ompiitudc of the generated paratus and not. in the theory, and it is not intended to limit the invention to such theory but rather to state the probable explanation of the operation of the apparatus.

Referring; to the drawing, Fig 1 represents one form of the invention in which a modulating and generating tube comprising the present improvement feeds into an amplifier for increasing the energy of the generated Waves. Figs. 2, 3, l and 5 illust ate other forms of circuit which may be substituted for the modulating and generating circuit of Fig. 1. Referring particularly to Fig. 1 tie ele vated conductor represents a suitable transmission circuit or conductor which is connected to earth at 11 through the induct s nce 12. The waves to be transmitted by the conductor 10 are produced by the generating tube which has connected thereto a tuned circuit including the inductance 13 and a condenser 14. Conductors extending from one side of thecondenser l4. and iron: an intermediate point in the inductance 13 lead to.

the input circuit of the tube 15, whose input electrodes comprise the usual heated filamentary cathode 16 and the grid or impedance controlling element 1?. The anode 18 is connected to the terminal of the inductance 13 remote from the terminal connected to the grid 17. The usual. battery placed in circuit with the anode and cathode.

The frequency of the oscillat ons in the output circuit is determined principally by the period of tuned circuit 13, 14-. and the association of this tuned circuit with the tube or discharge devicei 15 cause the oscillations to he maintained. A. resistance 31') and a battery 31. are included in the lead to the cathode 16, both these elements being shunted by the microphone Sound waves ac ing upon the microphone cause variin tions of potential of both the. impedanceontrollingz element 17 'ui'ul the anode 18 with respect to the cathode 18.- These speech frequency ariations causea corresponding variation in the high frcruieucy power or energy fed into the oscillatory circuit 13. 1%.

in accordance with this invention there lIlSt ted in the tuned circuit a preferably uonluctire and preferably adjustable 1'2- sistunce In operating the system to transmit electrical waves, the resistance l be increased to a value suitable to prod c good modulation. as cescrihed ahove. In general this will be when the system is onl upon the ocust;

slightly oscillatory and is therefore produc ing small amount of high frequency energy.

The energy of the oscillations produced may be directly transferred to a suitable transmitting conductor or antenna but in the present instance an amplifier 15 is provided by which the high frequency energy is increased. The coil 13 is for this purpose connected to the coil 23 included in the input circuit between the cathode 2. and the impedance controlling element 25 of the amplifier. tuned circuit. comprising a capacity 28 and the inductance 29 is connected hetween the cathode 24 and the anode 27, which constitute the output electrodes of the device This circuit is preferably tuned to'the same frequency as the circuit The electromagnetic coupling be tween coils 12 and 29 serves to transfer the amplified high frequency energy to the transmitting-conductor. Referring to the circuit of the modulating tube, it will be seen that the microphone serves to affect the impedance controlling element 17 and the anode 18 in an additive manner, whereby an increase in the potential of each thereof tends to cause an increase in the'intensity of the oscillations and vice versa.

In Fig 2 a transformer 40 replaces the resistance a0 and the battery 31. The secondary of this transformer is included in the lead to the cathode, While the primary is in circuit with the battery all and the microphone Sound waves acting upon the IlliClOf-llODG 4-2 causes a variation in amplitude of the oscillations generated in a man nor similar to that described in connection with 1. Reference characters common to Fig. 1 and the following figures represent corresponding elements.

In Fig. 3 an arrangement is shown in which the microphone acts to change the potential of the grid but not of the anode, in accordance with the speech waves. In this case the inductance 13 is divided in the middle and a large condenser 50, which has practically zero impedance for the high frequency currents, is inserted between the two 4 parts thereof". Since such a condenser will not he of zero impedance for speech lirequcncy currents, the trai'ismitter fifi'with its associated battery and transformer 53. rosy be connected in parallel to the com denser 5O shown. The potential variations of speech frequency are thus impressed grid nithout being also impressed upon the anode or plate oi the tube.

in the arrangement disclosed in Fig. 4:, the speech frequency variations of potential re impressed upon the grid through a transformer 60 which is located between the condenser lsf: and the grid 17.

Each of the systems described above depends for its modulating action upon the i energy dissipating means whereby the oscilassodiated therewith wherebyvariation of potential of one or more of the electrodes'of the modulating discharge device or. tube in accordance with speech. The arrangement of 5, however, does not operate upon this principle. The modula tion here is produced by the variable absorption of the high frequency waves by the microphone circuit. In order to accomplish this result, the resistance of the microphone or transmitter is introduced into the oscillating circuit by coupling a tuned circuit thereto. The tuned circuit 70 includes the condenser 71. microphones 7'2 and the inductance 73. The whole circuit; may be adjusted to be resonant at the Frequency to which the circuit 13, l t is tuned. The inductances 70 and 13 are elcctromagnetically coupled. Changes in the resistance of the micrcphone will cause corresponding changes in the amplitude of the oscillations produced in the tuned circuit. 13l4, owing to the variable dissipation of energy in the circuit 70, as a result of these changes of resistance.

In each system described above the fre quency of the high frequency pscillations may be determined by the setting of the condenser 14 and the value of the inductance 13.- The amplitude of oscillations may be adjusted from the greatest possible intensity almost to the critical point where oscillations cease, by adjusting resistance 35, without causing a substantial change in the fundamental frequency.

This a lication contains subject matter divided from my application Serial No. 51761, filed September 21, 1915, patented June 15, 1920,.No. 1343562.

The novel features inherent in the inycntion are defined in the appended claims.

What is claimed 'is:

- 1. A modulating system comprising an electron discharge device, means includinga tuned trcquency-determining loop circuit said device generates high frequency oscillations of a deiinite frequency determined principally by the tuning of said circuit, means including" a device for translating sound waves into electrical. variations for musing; the oscillations generated thereby to vary in accordance with said sound waves, and a resistance inthe tuned frequency-dctermihing circuit of such a value as to restrain to a comparatively small intensity the oscillations produced. I

2. A transmitting system comprising an electrondischargc device having an anode,

a cathode, and an in'ipedance varying element, a tuned series-resonant circuit coin prising inductance and capacity, parate leads from said inductance to said. anode, cathode and impedance varyingelement re spectively, said tuned circuit including lations generated are of a relatively small intensity as compared with their. intensity in the absence of such means.

3. A modulating system comprising an electron discharge device having an anode, a cathode and an impedance varying elemcnt, a tuned scries-rcsonantcircuit comprising inductance and capacity, separate leads from said inductance to said anode, cathode and impedance varyingelement respcctively, and a device associated therewith for varying in accordance with low frequency waves the oscillations produced by said device, said tuned circuit including a resistance of Such value as to maintain the working range of said discharge device upon a substantially straight portion of the space-voltage space-current characteristic thereof.

4. A transmitting system comprising an electron discharge device having an anode, a cathode and an impedance varying element, a tuned series resonant circuit oomprising inductance and capacity, and separate leads from said inductance to said anode, cathode and impedance varying element respectively, a device for varying at a relatively low frequency rate the oscillations produced by said discharge device, and a resistance included in said tuned circuit.

A telephone transmission system. comprising an evacuate electron discharge tube having an anode, a cathode and. an impedance vaiyingclement, an output circuit, an input circuit, a feedback connection between said circuits, and a tuned circuit associated with said device and with each of said circuits, a source of space current for energizing said device whereby oscillatory currents are-caused to be produced in said tuned circuit, a resistance of such value as to limit the produced oscillations to an amplitude small as compared with the maximum possible amplitude included in said tuned circuit, and device for varying in accordance with sound waves the potential of said impedance varying element with rospect to said cathode.

6. A telephone transmission system comprising an evacuated electron discharge tube hav ng an anode, a. cathode and an im pedance varying element, an output circuit, an input circuit, a teed-back connection be tween said circuits and a tuned circuit associated with said device, a source of space current, a resistance in said tuned circuit, and a device for varying in accordance with sound waves the potential of said anode with respect to said cathode.

' 7. A telephone transmission system com-- prising an evacuated electron discharge tube l ".V an anode, a cathode and an imtween said circuits and a tuned circuit as.

nee varyingelemcnt, an output circuit,

sociated with said tube, a source or space current, a resistance in said tuned circuit,

and a device for synchronously varying in charge device having a cathode, an anode,

and a control element, suitable circuits in cluding impedance elements, and a source of electromotiveforce of a given value for gen-- erating oscillations; and a device for introducing impedance variations of speech. frequency int-o the said system whereby the carrier frequency waves are aried in our plitude, said impedance elements being so designed, proportioned, and related to each other and to said device thatthe total oscillatory energ 1 is measurably less than is produced lay the same discharge device With the same given value of oleetromotive force when its circuits are adjusted for maximum total oscillatory energy output.

9. The method of producing oscillations olectromotive force whereby the carrier ire quency oscillations are generated; which;

comprises establishing oscillations of small energy in said device as compared with the energy when said device, supplied with an equal eleetromotive force, is producing the largest possible oscillations, and intrcduclllg the low frequency modulating Wave variation into the circuit connections of said. device In witness whereof, I hereunto subscribe my name this Zi'th'day of May, A. D. 1920.

RAYMOND A. HEISIN 

